drm: parse color format support for digital displays

EDID 1.4 digital displays report the color spaces they support in the
features block.  Add support for grabbing this data and stuffing it into
the display_info struct for driver use.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>